The present invention relates to a process for the preparation of resins based on polystyrene-divinylbenzene which are functionalized with primary amine or guanidine groups, and to novel resins which can be obtained by the use of this process.
These resins are used as bases, in particular as basic catalysts in liquid/solid heterogeneous phase reactions.
A process is known from U.S. Pat. No. 5,340,380, which consists in substituting the chlorine of a chloromethyl polystyrene-divinylbenzene resin with a substituted or unsubstituted guanidine and which makes it possible to obtain resins of general formula (A): ##STR2## represents the starting solid polystyrene-divinylbenzene resin support it being possible for R.sub.1, R.sub.2, R.sub.3 and R.sub.4 each to be a hydrogen, an alkyl group or an aromatic group.
Thus, U.S. Pat. No. 3,346,516 describes this technique of functionalization by reaction of a chloromethyl polystyrene-divinylbenzene resin with gruanidine or tetramethylguanidine in the presence of a lower alcohol and a solvent for swelling the copolymer such as tetra-hydrofuran, dioxane or diglyme.
In U.S. Pat. No. 5,028,259, the tetramethyLguanidine is placed in contact with a chloromethyl polystyrene-divinylbenzene resin in a mixture of toluene and tetrahydrofuran.
In U.S. Pat. No. 5,340,380, guanidines are reacted with chloromethyl resins of this same type in the presence of sodium hydroxide in a solvent consisting of ethanol or water.
Moreover, S. V. Luis, M. I. Burguete and B. Altava, Reactive & Functional Polymers, 26, 1995, 75-83 indicate that the ready chloromethylation of polystyrene resins and the high reactivity of the resulting benzyl sites allows the introduction of a large number of functional groups and explains the widespread use of these polymers. On the other hand, these authors comment that the reduced length of the methylene spacer arm reduces the mobility on the functional groups introduced and, in certain cases, makes it difficult for reactants, substrates and solvents to gain access to them. This situation may lead to a decrease in the activity of the functional groups when they are compared with their soluble correspondents. In certain cases, a marked improvement in the activity of these groups bound to the resin has been obtained when the active site is separated from the polymer skeleton by a suitable spacer arm. S. V. Luis et al. prepare polystyrene resins having spacer arms in the form of a linear aliphatic chain containing 6 or 9 methylene groups and bearing a hydroxyl group --OH at the end of the chain. This hydroxyl group is converted into a tosylate leaving group, the latter being replaced by substitution with a tertiary amine group.
In this synthesis, S. V. Luis et al. use functionalization of the polystyrene resin by a Friedel Crafts type reaction using the acid chloride derived from a monoalkyl ester of an alkanedioic acid.
This synthesis has the major drawback, of reducing both a tosylhydrazone group and an ester group by the double hydride LiAlH.sub.4 in tetrahydrofura THF. This reduction makes this synthetic route unattractive in terms of a large-scale industrial development of resins containing these --(CH.sub.2).sub.6 -- or --(CH.sub.2).sub.9 -- spacer arms.
Other authors have become interested in producing spacer arms in the form of a methylene chain. Thus, M. Tomoi, N. Kori and H. Kakiuchi, Reactive Polymers, 3, 1985, 341-349, introduce a long aliphatic chain onto polystyrene resins by alkylation with .omega.-bromoalkenes in the presence of trifluoromethanesulphonic acid.
However, this synthesis is limited to the preparation of polymers with a spacer arm which have a low degree of crosslinking (0-4%).
Starting with a chloromethyl polystyrene resin, G. D. Darling and M. J. Frechet, J. Org. Chem., 51, 1986, 2270-2276 have, for their part, obtained a --(CH.sub.2).sub.2 -- spaer arm which separates the resin fram a hydroxyl --OH at the end of the chain. This hydroxyl is converted, into tosylate and then, via the Gabriel reaction using potassium phthalimide and lastly hydrazine, into primary amine. However, this synthesis has the drawback of using n-butyllithium or lithium aluminium hydride.